Magnetic stabilization-wound cores



Filed 001;. 23, 1958 Fig.|.

Fig.2.

INvENToR James G. Ford United States Patent 3,074,039 MAGNETICSTABILIZATION-WOUND CORES James G. Ford, Sharon, Pa., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporaton ofPennsylvania Filed Oct. 23, 1958, Ser. No. 769,258 2 Claims. (Cl.335-213) The invention relates generally to cores for inductiveapparatus and more particularly to wound cores. This application is acontinuation-in-part of application Serial No. 574,170, filed March 27,1956.

Heretofore, in the manufacture of cores of all kinds, and particularlywound cores, the laminations are subjected to some distortion by theapplication 'of external forces. If the `distortion is great enough itintroduces stresses into the magnetic material which, if they cannot berelieved by further annealing, greatly increase the core losses inservice.

In the manufacture of transformer cores, and wound transformer cores inparticular, many methods have been tried to support the laminations,such for example, as the making of the core in a solid mass so that thelaminations are not subject to distortion and the building up ofstresses in the core iron.v

In order to provide a core which is a solid mass, it has lbeen commonpractice toimpregnate wound cores with' The organic materials and theiron have different coefficients of expansion and with changes intemperature, the expansion and contraction cause stresses to be lockedin the core iron.

In order to prevent the setting up of stresses in the core v iron andassure low exciting current and substantially no change from climatc andother conditions that may be found where such transformers are employed,it is desirable to find means for so supporting the laminations relativeto one another that there can be substantially no distortion of thelaminations and no building up of stresses in the core iron.

The object of the invention is to provide for supporting the laminationsof magnetic material of a core against distortion when subjected toexternal forces and the setting np of stresses in the magnetic materialwhich increase I core losses. It is also an object of the invention toprovide for the supporting of the laminations of a core of magneticmaterial whereby the setting up of permanent stresses in the magneticmaterial and the increasing of Operating losses is avoided.

'ice

FIG. 2 is va section of the core taken along the line II-II of FIG. 1.

Referring now to the drawing, and FIG. 1 in particular, the embodimentof the invention illustrated is a wound core. The wound core comprises anumber of turns of a cold rolled oriented Silicon iron strip. The numberof turns will depend on the specification to be met in the design of thetransforrner. The turns of the core are, in effect, laminationssuperimposed on one another.

In this embodiment the invention is applied to a wound core. However, itwill be appreciated that it can be applied to any type of core built upfrom individual laminations. The main function of the invention is to sosupport the laminations that there is no distortion of the metal inhandling the core which sets up stresses in the core iron and causes anincrease in core losses.

The core shown generally at 10 comprises -a plurality of turns orlaminations 11 which are in close contact with one another. Therefore,when pressures are applied to the external surface of the core they aretransmitted from one lamination to another and set up stresses in anumber of the laminations, depending on the distorting force ap- Iplied.

vnations, with changes in temperature is applied to the edges of thelaminations 11. The amount of cementitious material 12 applied may bevaried somewhat to meet design requirements. It has been found that inthe manufacture of most wound cores good results may be obtained by'applying the cementitious material 12 to a thickness of the order of3%4 inch to 1/16 inch. However, it is to be understood that these arenot positive limitations. The thicknesses prescribed have been arrivedat by experimentation and careful checking and will give good results.

It has been found that nearly any inorganic cementitious material whichwill air dry and on baking take on the characteristic of a ceramic maybe used. In tests made to determine the utility `of the invention,cementitious material such as sodium silicate and silica or some othersimilar filler was found to be satsfactory. Magnesium oxychloridecement, a cement sold under the trade name Portland cement and lithargeglycerine were also found to give good results.

The applying of the cementitious material may be effected in any wellknown manner. In the cores made a cement was prepared which was of suchconsistency that it could be applied by lmeans of a trowel or othersimilar tool. A layer of the required thickness was then applied to theedges of the laminations. When the cement was of the right consistencyit adhered and soon air dried. After the cement dried and became hard itwas subjected to a baking step to remove any unnecessary moisture. Thecore with the applied cementitious material may be baked in any suitableoven at temperatures Other objects of the invention will in part beobvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction,combination of elements and arrangement w of parts which will beexemplified in the construction hereconstructed in accordance with thefeatures of this invention; `and of 105 C. to 150 C.

When the cementitious material has been applied it will penetrate onlyslightly between the edges of the laminations. However, this penetrationtogether with its 'adherence to the edges of the metal is suflicient toenable the hardened cementitious material to support one lamination in apredetermined position relative to the adjacent lamination. j

In the manufacture of cores of this type it has been found that when theinorganic cementitious material has been properly hardened that thelaminations of the core are so supported that there is substantially nostresses introduced into the core iron by the ordinary handlingoperations which follow the application of the cementitious material.

The inorganic cementitious materials remain hard and sprgosa a U firmover the complete range of treating and operating temperatures.Therefore the laminations are supported in proper relationship to oneanother and stresses are not introduced into the iron during treatmentor operation.

The inorganic cementitious materials and the ferrous magneticlaminations disclosed and claimed herein each have a coefficient ofthermal expansion per degree Fahrenheit of from to 10-6. On the otherhand, organic resins have a coeflicient of thermal expansion per degreeFahrenheit of from 50 to 100 10-5 and even higher. Therefore, coresbonded with such organic resins are not completely satisfactory sinceboth core losses and exciting current are appreciably increased bystresses 'caused by differential expansion and contraction of the bondand ferrous magnetic laminations as the cores are alternately heated andcooled. Since inorganic cementitious mate- 'rials have a coefficient ofthermal expansion similar to that of the ferrous magnetic laminations,changes in temperature do not cause stresses to develop in cores bondedwith such cementitious materials.

In order to illustrate how effective the application of inorganiccementitious material to the edges of the laminations is in keeping downthe introduction of stresses into the iron by the Operations whichfollow in the manufacturing of transformers, a'table is givenhereinafter of the tests made on twelve wound cores supported by layersof hardened cementitious materials applied to the edges of thelaminations and two wound unbonded cores which were wound and verycarefully handled so as not to subject them to any distortion whichmight result in the building up of stresses in the iron. The unbondedcores were, in effect, laminated cores which had been annealed torelieve all stresses and handled thereafter to prevent the setting up ofany stresses.

Excting True. Watts Current in Loss Amperes Core Number of Cores havingIuorganc Cementitious Material Applied to the Edges of the Core:

1 .0365 .0077 .0350 .0072 .0350 .0070 .0375 0077 .0360 .0070 0385 .0074.0375 0078 .0360 .0076 .0360 .0074 0340 0068 0380 0078 0360 .0075 CoreNumber of Cores Without Cementitious Material Applied to the Edges ofthe Laminations:

13 (Unbonded) .0360 .0075 14 (Unbonded) 0345 0073 It will be observedfrom the foregoing table that the exciting current and the true Wattsloss in the first twelve cores which have inorganic cementitiousmaterial applied to the ends and hardened are substantially the same asthe exciting current and true Watts loss in the cores which have notbeen subjected to any distortion and, therefore, does not have anystresses locked in the iron. In making 'the test, it was found that ifthe cores without the inorganic cementitious material applied to theedges of the laminations were subjected to pressures, such as the'squeezng of them with the hand, that the exciting current increased toa marked extent. When the same pressure was applied to the corescarrying the hardened inorganic cementitious material there was nochange in the exciting 'current 'This clearly-shows the great advantagegained by supporting the laminations relative to one another by the useof the applied cementitious material which when air dried and baked takeon characteristics of a Ceramic.

This invention may be applied to cores for many types of transformersand other inductive apparatus. Considel' for instance currenttransformers used primarily for measuring purposes. It is highlyimportant that the exciting current be low to cut down cost of operationand that the exciting current remain constant under all measuringconditions in the interests of accuracy. Then a core of this type inwhich the laminations are supported relative to one another so thatstresses cannot be built up by distortion of lthe laminations is highlydesirable.

It will also be evident to anyone that inorganic cementitious materialsmay be applied without distorting the laminations in any way and,therefore, there will be no build-up of stresses in the iron in themanufacturing operation. It is also well known that inorganiccementitious materials once properly hardened and dried are not subjectto changes in weather conditions or to the atmospheres found in shopsand other places where such transformers may be employed. i

Since certain changes may be made in the above construction anddifferent embodiments of the invention could be made Vwithout departingfrom the scope thereof, it is intended that all matter contained in theabove description or shown in the accompanying drawing shall beinterpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a wound bonded core, in combination, a plu. rality of turns offerrous magnetic material in contact f with one another forming asubstantially cylindrical core,

a hardened nonresilient inorganic cementitious material selected from atleast one of the group consisting of sodium silicate and silica,magnesium oxychloride cement, Portland cement and litharge glycerineadhering to the edges and extending only slightly between the turns ofthe laminations, the hardened cementitious material cooperating with theferrous magnetic material to resist distortion of the laminationsupon-the application of outside forces and the setting up of stresses inthe ferrous magnetic materials with changes in temperature and therebycore losses.

2. In a bonded core of ferrous magnetic material, in combination, aplurality of turns of magnetic material in contact with one anotherforming aV core,4 a hardened non-resilient inorganic cementitiousmaterial selected from at least one of the group consisting of sodiumsilicate and silica, magnesium oxychloride cement, Portland cement andlitharge glycerine adhering to the edges and extending only slightlybetween the turns, the hardened inorganic cementitious material being ofa thick'- ness of the orderof lfig of an inch to 1/16 of an inch inthickness and cooperating with the ferrous magnetic material to resistdistortion when subjected to external forces and the hardened'cementitious material having a low coeflicient of thermalexpansioncorresponding to that of the ferrous magnetic material wherebyto minimize the setting up of stresses in the ferrous magnetic materialwith changes in temperature and thereby achieve low core losses.

References Cited in the file of this patent UNITED STATES PATENTS1.586.889 Elmen June l, 19.126 2,579,560 Ford Dec. 25, 1951 FOREIGNPATENTS 573,780' Great Britain V Dec. 5,l 1945

1. IN A WOUND BONDED CORE, IN COMBINATION, A PLURALITY OF TURNS OFFERROUS MAGNETIC MATERIAL IN CONTACT WITH ONE ANOTHER FORMING ASUBSTATIALLY CYLINDRICAL CORE, A HARDENED NON-RESILIENT INORGANICCEMENTITIOUS MATERIAL SELECTED FROM AT LEAST ONE OF THE GROUP CONSISTINGOF SODIUM SILICATE AND SILICA, MAGNESIUM OXYCHLORIDE CE-